It is generally desirable to reduce frictional resistance, also referred to as drag, of the hull of a ship, as this may increase the operating speed of the ship and/or reduce the fuel consumption.
JP10119875A discloses a system for reducing the frictional resistance a ship by forming an exhaust nozzle on a chamber installed on a surface of a spherical bow of a ship body, and by jetting air pressure supplied to the chamber by an air pressure supplying means, from the exhaust nozzle, so that the bubbles and an air layer are intervened on a boundary layer kept into contact with a submerged surface. The exhaust nozzle is formed by a front plate of a chamber which front plate has a number of pores. The air pressure is jetted into the water from the pores so as to generate a number of bubbles outside of the exhaust nozzle in such manner that they are spread along the flow lines and cover the submerged surface, whereby the friction is reduced.
GB2429435A discloses a vessel hull having an air lubrication apparatus which comprises an air pump for supplying pressurised air to a porous membrane attached to the exterior of the hull and keel, or a system of air ducts attached to the keel and hull of the vessel, or mounted within the hull of the vessel.
JP10175587A discloses a method wherein small air bubbles are fed in a boundary layer so as to reduce the generation of frictional resistance of a hull. The bubbles are blown out of a porous plate in which a number of small ports are formed at given pitches.
CN2652812Y discloses a micro bubble generator used for drag reduction comprising a cavity, a connection pipeline, a pressure air power machine and a porous silicon plate
However, even though the above prior art systems disclose the generation of bubbles by means of bubble generators which can be fitted to a ship's hull, it remains a problem to provide a method for generating micro-bubbles for efficiently reducing the drag or frictional resistance of a ship's hull during different operational conditions, e.g. different speeds, water temperature, draught, and/or the like.